cheetarah has it pretty much covered.
I'll add a few points though...
I don't think it's ever too early to start the process. This time last year I started visiting schools, brainstorming about what to write about in my essays, and thinking about who to select as recommenders.
As far as the essays and application itself, you're still several months away. Last year, Columbia was one of the first schools to go live with its essay questions. They were released in early May. I know for Kellogg and Booth, it was late summer (July-August). The deadlines for this year will probably be similar to last year's. Take a look at the threads for each school to get a good estimate.
cheetarah makes a good point about which round to apply in. I applied in R1 everywhere because 1.) I wanted to seal my fate as soon as possible, and 2.) i think there are slightly better odds in R1 (just my opinion).
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